Chromium catalyst compositions

ABSTRACT

Chromium catalyst compositions are provided. Theses chromium catalyst compositions can be used to polymerized olefins. The resulting polymerization product can have improved properties.

BACKGROUND OF THE INVENTION

This invention is related to the field of chromium catalystcompositions.

It is known in the art that as the density of a polyolefin compositionincreases, the chemical resistance, tensile strength, and stiffnessincrease, but the permeability, toughness, and environmental stresscrack resistance decrease. This can present a problem for example, whenboth a high density and a high environmental stress crack resistance aredesired.

This invention provides a solution to this problem of competingperformance factors.

SUMMARY OF THE INVENTION

It is an object of this invention to provide chromium catalystcompositions.

It is another object of this invention to provide chromium catalystcompositions useful in polymerizing olefins.

It is another object of this invention to provide chromium catalystcompositions useful in polymerizing ethylene.

It is another object of this invention to provide chromium catalystcompositions useful in copolymerizing ethylene and at least one otherolefin.

It is another object of this invention to provide chromium catalystcompositions useful in copolymerizing ethylene and 1-hexene.

In accordance with this invention chromium catalyst compositions areprovided. These chromium catalyst compositions comprise at least twochromium catalyst systems. These chromium catalyst systems comprisechromium and a support, wherein the support comprises silica, andwherein the supports of at least two of the systems have an average poreradius difference sufficient to preferentially introduce a non-ethylenecomonomer into the higher molecular weight portion of a resultingcopolymer.

In accordance with another embodiment of this invention chromiumcatalyst compositions are provided (hereafter referred to as "embodimentX") . These chromium catalyst compositions comprise at least twochromium catalyst systems. These chromium catalyst systems comprisechromium and a support, wherein the support consists essentially ofsilica and titania, and wherein at least two of the supports have anaverage pore radius difference of about 25 angstroms.

In accordance with another embodiment of this invention chromiumcatalyst compositions are provided (hereafter referred to as "embodimentY"). These chromium catalyst compositions comprise at least two chromiumcatalyst systems wherein:

(a) one of these chromium catalyst systems comprises chromium and asupport,

wherein the support consists essentially of silica and titania, andwherein the support has sn average pore radius less than about 85angstroms, and wherein the support has a pore volume less than about 1.2cubic centimeters per gram, and

wherein this chromium catalyst system is subjected to at least one ofthe following treatments (1) reduced and reoxidized, (2) titanated, and(3) activated at a high temperature;

(b) one of these chromium catalyst systems comprises chromium and asupport,

wherein the support consists essentially of silica, and wherein thesupport has an average pore radius greater than about 85 angstroms, andwherein the support has a pore volume greater than about 1.5 cubiccentimeters per gram, and

wherein this chromium catalyst system is subjected to at least one ofthe following treatments (1) activated at a low temperature, and (2)contacted with a fluorine compound.

In accordance with another embodiment of this invention chromiumcatalyst compositions are provided (hereafter referred to as "embodimentZ"). These chromium catalyst compositions comprises at east two chromiumcatalyst systems wherein:

(a) one of these chromium catalyst systems comprises chromium and asupport,

wherein the support consists essentially of silica and titania, andwherein the support has an average pore radius greater than about 85angstroms, and wherein the support has a pore volume greater than about2 cubic centimeters per gram, and

wherein this chromium catalyst system is subjected to at least one ofthe following treatments (1) reduced and reoxidized, (2) titanated, and(3) activated at a high temperature;

(b) one of these chromium catalyst systems comprises chromium and asupport,

wherein the support consists essentially of silica, and wherein thesupport has an average pore radius less than about 85 angstroms, andwherein the support has a pore volume less than about 1.7 cubiccentimeters per gram, and

wherein this chromium catalyst system is reduced.

In accordance with another embodiment of this invention each of theabove embodiments can be contacted with one or more different olefins,under polymerization conditions, to produce a polymer or copolymer.

This invention as disclosed in this application can be suitablypracticed in the absence of any steps, components, compounds, oringredients not disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

In general, the chromium catalyst compositions used in this inventioncomprise at least two chromium catalyst systems. These chromium catalystsystems comprise a chromium component and a support component comprisingsilica. The term "support component" is not meant to be construed as aninert component of the chromium catalyst system.

The supports used in the chromium catalyst systems of this inventioncan:

(1) comprise silicas

(2) consist essentially of silica and titania; or

(3) consist essentially of silica.

These supports are known in the art and are disclosed in U.S. Pat. Nos.2,825,721; 3,225,023; 3,226,205; 3,622,521; 3,625,864; 3,780,011;3,887,494; 3,900,457; 3,947,433; 4,053,436; 4,081,407; 4,151,122;4,177,162; 4,294,724; 4,296,001; 4,392,990; 4,402,864; 4,405,501;4,434,243; 4,454,557; 4,735;931; 4,981,831; 5,037,911; the entiredisclosures of which are hereby incorporated by reference. However, itshould also be noted that these types of supports are availablecommercially from such sources as the Davison Chemical Division of theW. R. Grace Corporation.

The amount of silica present in the support is generally greater thanabout 80 weight percent where the weight percent is based on the weightof the support. However, it is preferred that the amount of silica inthe support is from about 90 to about 100 weight percent. The remainingportion, if any, can be selected from alumina, titania, boria, magnesia,thoria, zirconia, and mixtures of two or more thereof.

When the support consists essentially of silica and titania, the amountof silica in the support is generally greater than about 80 weightpercent where the weight percent is based on the weight of the support.However, it is also preferred that the amount of titania used in thesupport be greater than about 0.1 weight percent. It is more preferredthat the amount of titania used is from about 1 weight percent to about20 weight percent and it is most preferred that the amount be from about1 weight percent to about 10 weight percent.

In "embodiment X" of this invention, the chromium catalyst compositionscomprise at least two chromium catalyst systems. These chromium catalystsystems comprise chromium and supports that consists essentially ofsilica and titania. These supports should have an average pore radiusdifference of about 25 angstroms. However, it is preferred that theaverage pore radius difference be from about 25 angstroms to about 400angstroms and it is most preferred if the average pore radius differenceis from 50 angstroms to 300 angstroms. The average pore radius of eachsupport can be determined by nitrogen sorption by a person with ordinaryskill in the art. For example, the following references can be used"Adsorption, Surface Area and Porosity" by S. J. Gregg and K. S. W.Sing, Academic Press, London (1982); and "Introduction to Powder SurfaceArea" by S. Lowell, J. Wiley & Sons, New York, N.Y. (1979); the entiredisclosures of which are hereby incorporated by reference.

In "embodiment Y" of this invention the chromium catalyst compositionscomprise at least two chromium catalyst systems. One of these chromiumcatalyst systems comprises chromium and a support wherein the supportconsists essentially of silica and titania. Another of these chromiumcatalyst systems comprises chromium and a support wherein the supportconsists essentially of silica.

The supports used in "embodiment Y" are further described as follows:

(1) the supports that consist essentially of silica and titania shouldhave an average pore radius less than about 85 angstroms;

however, it is preferred that they have an average pore radius fromabout 25 to about 85 angstroms and it is most preferred that they havean average pore radius from 30 to 80 angstroms;

furthermore, the supports that consist essentially of silica and titaniashould have a pore volume less than about 1.2 cubic centimeters pergram; however, it is preferred that they have a pore volume frown about0.6 to about 1.2 cubic centimeters per gram and it is most preferredthat they have a pore volume from 0.8 to 1.15 cubic centimeters pergram;

hereafter, these types of supports will be referred to as "type Asupports";

(2) the supports that consist essentially of silica should have anaverage pore radius greater than about 85 angstroms; however, it ispreferred that they have an average pore radius from about 85 to about1000 angstroms and it is most preferred that they have an average poreradius from 90 to 500 angstroms;

furthermore, the supports that consist essentially of silica should havea pore volume greater than about 1.5 cubic centimeters per gram;however, it is preferred that they have a pore volume from about 1.5 toabout 4 cubic centimeters per gram and it is most preferred that theyhave a pore volume from 1.5 to 3 cubic centimeters per gram;

hereafter, these types of supports will be referred to as "type Bsupports."

In "embodiment Z" of this invention the chromium catalyst compositionscomprise at least two chromium catalyst systems. One of these chromiumcatalyst systems compresses chromium and a support wherein the supportconsists essentially of silica and titania. Another of these chromiumcatalyst systems comprises chromium and a support wherein the supportconsists essentially of silica.

The supports used in "embodiment Z" are further described as follows:

(1) the supports that consist essentially of silica and titania shouldhave an average pore radius greater than about 85 angstroms; however, itis preferred that they have an average pore radius from about 85 toabout 1000 angstroms and it is most preferred that they have an averagepore radius from 90 to 500 angstroms;

furthermore, the supports that consist essentially of silica and titaniashould have a pore volume greater than about 2 cubic centimeters pergram; however, it is preferred that they have a pore volume from about 2to about 4 cubic centimeters per gram and it is most preferred that theyhave a pore volume from 2 to 3 cubic centimeters per gram;

hereafter, these types of supports will be referred to as "type Csupports";

(2) the supports that consist essentially of silica should have anaverage pore radius less than about 85 angstroms; however, it ispreferred that they have an average pore radius from about 25 to about85 angstroms and it is most preferred that they have an average poreradius from 30 to 80 angstroms;

furthermore, the supports that consist essentially of silica should havea pore volume less than about 1.7 cubic centimeters per gram; however,it is preferred that they have a pore volume from about 0.6 to about 1.7cubic centimeters per gram and it is most preferred that they have apore volume from 0.8 to 1.3 cubic centimeters per gram;

hereafter, these types of supports will be referred to as "type Dsupports."

The chromium component of the chromium catalyst systems that are part ofthe chromium catalyst compositions of this invention can be any suitablechromium compound that facilitates the polymerization of olefins.Suitable examples of chromium compounds included, but are not limitedto, chromium nitrate, chromium acetate, chromium trioxide, and mixturesof two or more said chromium compounds. The amount of chromium compoundthat is combined with the support is from about 0.1 weight percent toabout 5 weight percent. It is preferred that the amount be from about0.2 weight percent to about 5 weight percent and it is most preferredthat the amount be from 0.5 to 2 weight percent where the weight percentis based on the weight of the chromium compound and the support.

The chromium compound can be combined with the support in any mannerknow in the art. Examples of combining the chromium compound with thesupport can be found in the above cited and incorporated patents.Preferred methods of combining the chromium compound with the supportare disclosed in U.S. Pat. Nos. 3,976,632; 4,248,735; 4,297,460; and4,397,766; the entire disclosures of which are hereby incorporated byreference. These patents disclose impregnating the support withanhydrous chromium compounds.

In "embodiment Y" of this invention, chromium catalyst systems thatcomprise chromium and "type A supports" are (1) reduced and reoxidized,(2) titanated, and/or (3) activated at a high temperature. Additionally,in "embodiment Y" of this invention, chromium catalyst systems thatcomprise chromium and "type B supports" are (1) activated at a lowtemperature, and/or (2) contacted with a fluorine compound. At least aportion of the chromium used in this embodiment of the invention ispreferably in the hexavalent state.

In "embodiment Z" of this invention, chromium catalyst systems thatcomprise chromium and "type C supports" are (1) reduced and reoxidized,(2) titanated, and/or (3) activated at a high temperature. Additionally,in "embodiment Z" of this invention, chromium catalyst systems thatcomprise chromium and "type D supports" are reduced. At least a portionof the chromium used with the "type C supports" is preferably in thehexavalent state. On the other hand, at least a portion of the chromiumused with the "type D supports" is preferably in the divalent state.

The chromium catalyst systems used in this invention can be reduced andreoxidized in accordance with any manner known in the art that willreduce at least a portion of the chromium to a lower valence state andthen reoxidized at least a portion of the chromium to a higher valencestate. Suitable examples of this type of procedure can be found in U.S.Pat. Nos. 4,151,122 and 4,177,162 the entire disclosures of which arehereby incorporated by reference.

The chromium catalyst systems used in this invention can be titanated inaccordance with any manner known in the art that will combine a titaniumcompound with the chromium catalyst system. Suitable examples of thistype of procedure can be found in U.S. Pat. Nos. 3,622,521; 3,625,864;3,780,011; 4,368,303; 4,402,864; 4,424,320; and 4,429,724; 4,434,243;the entire disclosures of which are hereby incorporated by reference.

The chromium catalyst systems used in this invention can be reduced inaccordance with any manner known in the art that will reduce at least aportion of the chromium to a lower valence state. Suitable examples ofthis type of procedure can be found in U.S. Pat. No. 4,735,931 theentire disclosure of which is hereby incorporated by reference. It ispreferred that the reducing composition be carbon monoxide.

The chromium catalyst systems used in this invention can be contactedwith a fluorine compound in accordance with any manner known in the artthat will incorporated fluorine onto or into the chromium catalystsystem. Suitable examples of this type of procedure can be found in U.S.Pat. Nos. 2,825,721; 4,806,513; and 5,037,911; the entire disclosures ofwhich are hereby incorporated by reference.

The chromium catalyst systems used in this invention can be activated inaccordance with any manner known in the art that will contact an oxygencontaining ambient with a chromium catalyst system. Suitable examples ofthis type of procedure can be found in U.S. Pat. Nos. 3,887,494;3,900,457; 4,053,436; 4,081,407; 4,296,001; 4,392,990; 4,405,501;4,981,831; the entire disclosures of which are hereby incorporated byreference.

In general, activation at high temperature is conducted at a temperaturegreater than about 700 degrees Celsius and activation at low temperatureis conducted at a temperature less than about 700 degrees Celsius.However, it is preferred that activation at a high temperature beconducted at a temperature between about 750 degrees Celsius and about900 degrees Celsius; and most preferably it is conducted at atemperature between 800 degrees Celsius and 900 degrees Celsius. It isalso preferred that activation at a low temperature be conducted at atemperature between about 450 degrees Celsius and about 700 degreesCelsius; and most preferably it is conducted at a temperature between500 degrees Celsius and 650 degrees Celsius.

Once the chromium catalyst systems are made they may be combinedtogether in any manner known in the art. For example, they can be dryblended together in a mixer or added to a feed stream that leads to areactor. It is important to note that by varying the amounts of eachchromium catalyst system included in the chromium catalyst composition,it is possible to vary the amount of comonomer incorporated into theresulting copolymer composition. Furthermore, by varying the amount ofeach chromium catalyst system included in the chromium catalystcomposition, the density of the resulting polymer can be modified moreindependently of the melt index than was previously known for thesetypes of chromium catalyst systems. Additionally, by varying the amountof each chromium catalyst system included in the chromium catalystcomposition, or by varying the average pore radius difference betweenthe supports in the chromium catalyst compositions, it is possible topreferentially introduce a non-ethylene comonomer into the highermolecular weight portion of a resulting copolymer. In general, thehigher molecular weight portion can be determined using data collectedby gel permeation chromatography using equipment readily available fromcommercial sources. The higher molecular weight portion is that portiongreater than the weight average molecular weight. Preferentiallyintroducing a non-ethylene comonomer into the higher molecular weightportion of a resulting copolymer means that a major portion of thecomonomer is located in the higher molecular weight portion. This can bedetermined by calculating the number of short chain alkyl branches inthe polymer. For example, in an ethylene an 1-hexene copolymer thenumber of butyl branches will give an indication of the amount of1-hexene comonomer incorporated into the polymer.

The chromium catalyst compositions used in this invention can becontacted with one or more olefins under polymerization conditions toproduce homopolymer or copolymer compositions. Suitable olefins include,but are not limited to, ethylene, propylene, 1-butene,3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene,1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene and mixtures of two ormore of said olefins. Particularly preferred is ethylene. Additionally,a particularly preferred combination of olefins to use is ethylene and1-hexene. These two olefins are particularly preferred at this timebecause these olefins copolymerized especially well with the chromiumcatalyst compositions disclosed in this invention.

Various polymerization schemes are known in the art. For example, U.S.Pat. Nos. 2,825,721; 3,152,872; 3,172,737; 3,203,766; 3,225,023;3,226,205; 3,242,150; 3,248,179; and 4,121,029; (the entire disclosuresof which are hereby incorporated by reference) disclose severalpolymerization schemes. A particularly preferred polymerization methodis a slurry or particle form polymerization method. This method isdisclosed for example, in U.S. Pat. No. 3,248,179. Two preferred slurrypolymerization techniques are those employing a loop reactor and thoseemploying a plurality of stirred reactors either in series, parallel orcombinations thereof.

EXAMPLE

This example is provide to further assist a person skilled in the artwith understanding this invention. The particular reactants, catalystsand conditions are intended to be generally illustrative of thisinvention and are not meant to be construed as unduly limiting thereasonable scope of this invention.

The polymerizations were conducted in a 87 liter, 15.2 centimeterdiameter, pipe loop reactor. The polymer was recovered in a flashchamber. A Vulcan dryer was used to dry the polymer.

Ethylene that had been dried over alumina was used as the polymerizationmonomer. Isobutane that had been degassed by fractionation and driedover alumina was use as the polymerization diluent. Triethylboron wasalso used as a cocatalyst.

A "Quantachrome Autosorb-6 Nitrogen Pore Size Distribution Instrument"was used to determined the average pore radius and pore volumes of thesupports. This instrument was acquired from the QuantachromeCorporation, Syosset, N.Y. The average pore radius was calculated usingthe following formula: ##EQU1##

In run number one the following chromium catalyst compositions wereused:

(1) a commercially available chromium catalyst system purchased from theW. R. Grace Corporation. This chromium catalyst system was the MagnaporeCatalyst. It had an average pore radius of about 94 angstroms and a porevolume of about 2.1 cubic centimeters per gram. It also had a chromiumcontent of about 1 weight percent based on the weight of the chromiumcatalyst system. This chromium catalyst system was reduced at atemperature of about 845 degrees Celsius and then reoxidized at atemperature of about 650 degrees Celsius;

(2) a commercially available chromium catalyst system purchased from theW. R. Grace Corporation. This chromium catalyst system was the 969IDcatalyst. It had an average pore radius of about 78 angstroms and a porevolume of about 1.1 cubic centimeters per gram. It also had a chromiumcontent of about 1 weight percent based on the weight of the chromiumcatalyst system. This chromium catalyst system was activated at atemperature of about 540 degrees Celsius and then reduced at atemperature of about 370 degrees Celsius with carbon monoxide. Thiscatalyst system produce mono-1-hexene during the polymerization ofethylene.

These two catalyst systems were then blended together and use topolymerize ethylene. Additional information concerning thispolymerization and the results obtain are presented in table E1.

                  TABLE E1                                                        ______________________________________                                        1   Reactor Residence Time                                                                              1.23    hours                                       2   Reactor Temperature   107°                                                                           C.                                          3   Triethylboron Amount in Parts per                                                                   2.7                                                     Million by Weight Based on the                                                Isobutane Diluent                                                         4   Melt Indexes of the Copolymer                                                                       0.35    g/10 mins.                                      According to ASTM-D-1238                                                  5   Density of Copolymer According                                                                      0.9555  g/cc                                            to ASTM-D-1505                                                            6   Environmental Stress Crack                                                                          220     hours                                           Resistance of the Copolymer                                                   According to ASTM-D-1693                                                  ______________________________________                                    

In run number two the following chromium catalyst compositions wereused:

(1) a commercially available chromium catalyst system purchased from theW. R. Grace Corporation. This chromium catalyst system was the MagnaporeCatalyst. It had an average pore radius of about 94 angstroms and a porevolume of about 2.1 cubic centimeters per gram. It also had a chromiumcontent of about 1 weight percent based on the weight of the chromiumcatalyst system. This chromium catalyst system was reduced at atemperature of about 870 degrees Celsius and then reoxidized at atemperature of about 590 degrees Celsius;

(2) a commercially available chromium catalyst system purchased from theW. R. Grace Corporation. This chromium catalyst system was the 969IDcatalyst. It had an average pore radius of about 78 angstroms and a porevolume of about 1.1 cubic centimeters per gram. It also had a chromiumcontent of about 1 weight percent based on the weight of the chromiumcatalyst system. This chromium catalyst system was activated at atemperature of about 650 degrees Celsius and then reduced at atemperature of about 370 degrees Celsius with carbon monoxide. Thiscatalyst system produce mono-1-hexene during the polymerization ofethylene.

These two catalyst systems were then blended together and use tocopolymerize ethylene and mono-1-hexene. Additional informationconcerning this polymerization and the results obtained is presented intable E2.

                  TABLE E2                                                        ______________________________________                                        1   Reactor Residence Time                                                                              1.22    hours                                       2   Reactor Temperature   96°                                                                            C.                                          3   Triethylboron Amount in Parts per                                                                   2.57                                                    Million by Weight Based on the                                                Isobutane Diluent                                                         4   Melt Indexes of the Copolymer                                                                       0.09    g/10 mins.                                      According to ASTM-D-1238                                                  5   Density of Copolymer According                                                                      0.9551  g/cc                                            to ASTM-D-1505                                                            6   Environmental Stress Crack                                                                          262     hours                                           Resistance of the Copolymer                                                   According to ASTM-D-1693                                                  ______________________________________                                    

For comparison purposes a commercially available chromium catalyst wasobtain from the Davison Corporation (tradename of 969MS). This catalysthad an average pore radius of about 94 angstroms and a pore volume ofabout 1.5 cubic grams per centimeter, Under polymerization conditionssimilar to the above it produced a copolymer having the followingcharacteristics:

    ______________________________________                                        Melt index of   0.3 grams/10 minutes.                                         Density of      0.957 grams/cubic centimeter                                  ESCR of         100 hours                                                     ______________________________________                                    

It can be seen from the above that a copolymer having both a highdensity and a high environmental stress crack resistance can be obtainedby using this invention. This is especially apparent when comparing thecopolymer produced from the 969MS catalyst to the copolymers producedaccording to this invention.

That which is claimed is:
 1. A process comprisingproducing a copolymerby copolymerizing ethylene and at least one non-ethylene comonomer,wherein said copolymer has a high molecular weight portion that has amolecular weight greater than the weight average molecular weight ofsaid copolymer with a chromium catalyst composition that comprises atleast two chromium catalyst systems, wherein each said chromium catalystsystem comprises chromium and a support, and wherein each supportcomprises silica, and wherein at least two of said chromium catalystsystems have supports that have an average pore radius differencesufficient to preferentially introduce said non-ethylene comonomer intosaid high molecular weight portion.
 2. A process according to claim 1wherein said non-ethylene comonomer is selected from the groupconsisting of propylene, 1-butene, 3-methyl-1-butene, 1-pentene,3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 3-ethyl-1-hexene,1-octene, 1-decene, and mixtures of two or more thereof.
 3. A processaccording to claim 1 wherein said non-ethylene comonomer is 1-hexene. 4.A process comprisingproducing a copolymer by copolymerizing ethylene andat least one non-ethylene comonomer with a chromium catalyst compositionthat comprises at least two chromium catalyst systems, wherein each saidchromium catalyst system comprises chromium and a support, and whereineach support consists essentially of silica and titania, and wherein atleast two of said chromium catalyst systems have supports that have anaverage pore radius difference of about 25 angstroms.
 5. A processaccording to claim 4 wherein said non-ethylene comonomer is selectedfrom the group consisting of propylene, 1-butene, 3-methyl-1-butene,1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene,3-ethyl-1-hexene, 1-octene, 1-decene, and mixtures of two or morethereof.
 6. A process according to claim 4 wherein said non-ethylenecomonomer is 1-hexene.
 7. A process comprisingproducing a copolymer bycopolymerizing ethylene and at least one non-ethylene comonomer with achromium catalyst composition that comprises at least two chromiumcatalyst systems, wherein:(a) at least one of said chromium catalystsystems comprises chromium and a support, and wherein said supportconsists essentially of silica and titania, and wherein said support hasan average pore radius less than about 85 angstroms, and wherein saidsupport has a pore volume less than about 1.2 cubic centimeters pergram, and wherein this chromium catalyst system is subjected to at leastone of the following treatments (1) reduced and reoxidized (2) titanatedand (3) activated at a high temperature; and (b) at least one of saidchromium catalyst systems comprises chromium and a support, and whereinsaid support consists essentially of silica, and wherein the support hasan average pore radius greater than about 85 angstroms, and wherein saidsupport has a pore volume greater than about 1.5 cubic centimeters pergram, and wherein this chromium catalyst system is subjected to at leastone of the following treatments (1) activated at a low temperature, and(2) contacted with a fluorine compound.
 8. A process according to claim7 wherein said non-ethylene comonomer is selected from the groupconsisting of propylene, 1-butene, 3-methyl-1-butene, 1-pentene,3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 3-ethyl-1-hexene,1-octene, 1-decene, and mixtures of two or more thereof.
 9. A processaccording to claim 4 wherein said non-ethylene comonomer is 1-hexene.10. A process comprisingproducing a copolymer by copolymerizing ethyleneand at least one non-ethylene comonomer with a chromium catalystcomposition that comprises at least two chromium catalyst systems,wherein:(a) at least one of said chromium catalyst systems compriseschromium and a support, and wherein said support consists essentially ofsilica and titania, and wherein said support has an average pore radiusless than about 85 angstroms, and wherein said support has a pore volumeless than about 1.2 cubic centimeters per gram, and wherein thischromium catalyst system is subjected to at least one of the followingtreatments (1) reduced and reoxidized (2) titanated and (3) activated ata high temperature; and (b) at least one of said chromium catalystsystems comprises chromium and a support, and wherein said supportconsists essentially of silica, and wherein the support has an averagepore radius greater than about 85 angstroms, and wherein said supporthas a pore volume greater than about 1.5 cubic centimeters per gram, andwherein this chromium catalyst system is activated and then reduced. 11.A process according to claim 10 wherein said non-ethylene comonomer isselected from the group consisting of propylene, 1-butene,3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene,1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, and mixtures of two ormore thereof.
 12. A process according to claim 10 wherein saidnon-ethylene comonomer is 1-hexene.